Basic mechanisms of synaptic integration will be explored at the parallel fiber synapse onto the rat cerebellar Purkinje neuron. Purkinje neurons were chosen for their dendrites, which have the most complex known arborization in the animal kingdom and receive about 100,000 inputs per Purkinje neuron. Methods to be used include whole-cell patch clamp recording, focal photolysis of caged compounds, video-rate confocal fluorescence microscopy of calcium-sensitive dyes, and advanced image processing. The hypothesis to be tested is: synaptic activity produces calcium and other second messenger signals that are localized in space and time, and this signal localization sets parameters of dendritic integration and synaptic plasticity. These studies will provide a greater understanding of how synaptic integration and plasticity contribute to thought, learning, and memory.